He penned three original series episodes. All of these were based on short stories written by him previously. "What Are Little Girls Made Of?" came out from three of his stories, most notably Queen of the Metal Men, "Catspaw" was loosely based on his 1957 story Broomstick Ride, while "Wolf in the Fold" was adapted from the 1943 story Yours Truly, Jack the Ripper, which was previously adapted to an episode of Thriller in 1961. Two of his episodes ("What Are Little Girls Made Of?" and "Catspaw") make mentions of the "Old Ones", a term frequently used by Lovecraft in his stories.

Bloch got disillusioned with Star Trek at the end of the second season, mostly because of the change in management under the new Paramount regime, and never returned to write more episodes after "Wolf in the Fold". (These Are the Voyages: TOS Season Two)